Incumbents have all of the following advantages over their challengers EXCEPT

challengers have a clean political record, but the incumbents do not.

Explanation:

Incumbents simply refers to the person that's holding a particular position or office while the challenger is the person challenging the incumbents that want to take over their position.

While the incumbents have the experience in the role, we should note that the advantage that the Challenger has over the incumbent is that he or she will have a political record that's still clean. In a case whereby the incumbent have done some nasty things that the people didn't like, this may be of immense advantage to the challenger as he or she still has a clean record.